This disclosure relates to improved pyrotechnic igniters. In particular, this disclosure relates to pyrotechnic igniters usable, for example, to ignite a pyrotechnic material and, in turn, cause the heating of energetic devices such as thermal batteries. The invention, however, is not limited to use with thermal batteries, but is applicable to various situations in which a pyrotechnic igniter may be useful in generating heat and/or pressure.
Pyrotechnic igniters are devices containing a pyrotechnic material that is ignited causing a chain reaction resulting in the expulsion of hot gases and/or particles from the igniter. The expelled hot gases and/or particles are then used to ignite a later stage of a pyrotechnic train or to perform work.
The pyrotechnic material is often ignited via electrical initiation. In particular, electrical pyrotechnical initiators are initiators that use a bridge (a resistance element), which heats up by electrical current passing through the bridge, in order to ignite the pyrotechnic material. An example of a pyrotechnic initiator is the coin-shaped electrical pyrotechnic initiator illustrated in FIG. 1.
The coin-shaped initiator 1 of FIG. 1 includes a circular housing 2 having a top opening 12 and a disc closure 3 that covers the top opening 12 after a non-conductive ignitable material 4 and conductive ignitable material 5 have been loaded into the housing 2. Lead wires 6 are inserted in the Y-direction 10 into the housing 2. A glass/metal seal 8 surrounds the lead wires 6 entering into the housing 2. A bridge element (not shown) is disposed within an interior, bottom portion of the housing 2. The non-conductive material 4 is loaded within the interior of the housing 2. Further, the non-conductive material 4 is loaded into the housing 2 in an X-direction 9 perpendicular to the Y-direction 10. Specifically, the non-conductive material 4 is loaded into the housing 2 via the top opening 12. The conductive material 5 is loaded into the housing in the same X-direction 9 as the non-conductive material 4 and on top of the non-conductive material 4. Additionally, a weakened area 11 is formed in a top surface 13 of the disc closure 3. In the coin-shaped igniter, current is conducted via the lead wires 6 through the bridge element 7. The bridge element (usually a metal wire or foil) heats up due to its resistance, causing the non-conductive material 4 and the conductive material 5 to ignite. A pressure increase caused by ignition of the materials 4, 5 causes the weakened area 11 to rupture in the X-direction 9 (rupture direction 14), which is perpendicular to the Y-direction 10.
The non-conductive (electrically-isolative) material 4 is provided in contact with the bridge element to electrically isolate the bridge element from the housing 2 and the disc closure 3 so that any charge (including electro-static charge) inadvertently applied to the external housing (including the disc closure 3) does not unintentionally cause the bridge element to heat up. For example, if only electrically conductive ignitable material 5 is provided in the igniter, charges inadvertently applied to the external housing might cause current to flow through (and heat up) the bridge element and the pyrotechnic materials 4 , 5 because the external housing (including the disc closure 3) is electrically conductive. Thus, it may be desirable or necessary to electrically isolate the pyrotechnic materials 4, 5 from the external housing.
Another typical electrical pyrotechnic igniter is an axial igniter having a cylindrical housing and a header. The cylindrical (barrel-shaped) housing includes an end opening into which a conductive pyrotechnic material and then a non-conductive pyrotechnic material are loaded. The header has lead wires attached to a first end and a bridge element attached to a second end. The second end of the header is inserted into the housing containing the conductive and non-conductive pyrotechnic materials such that the bridge element contacts the non-conductive material and the header is sealed to the housing end opening. An opposite (second) end of the housing, opposite the first end opening, includes a weakened area. When current is conducted through the lead wires of the axial igniter and through the bridge element, the bridge element heats up, causing the pyrotechnic material to ignite. The pressure increase caused by ignition of the pyrotechnic material causes the weakened area to rupture in an axial direction that is parallel to the direction of insertion of the lead wires into the header.